The present invention generally relates to an ink composition and to a method of making the ink composition. More specifically, the present invention relates to an ink composition that may be used in ink jet printing and to a method of making this ink composition. The present invention further relates to a method of printing the ink composition on a variety of recording media, such as fibrous recording media, porous recording media, and hydrophobic recording media.
Ink jet printing is a non-impact printing process in which ink droplets are formed and thereafter deposited on a print medium in a particular order to form an image on the print medium. The low cost and high quality of the printed output in combination with the relatively noise-free operation of ink jet printers have made ink jet printing a popular and economical alternative to other types of printing in consumer, office, and industrial settings.
Ink jet printing generally involves the creation and ejection of tiny droplets of ink. There are a number of different techniques currently available for creating and ejecting the ink droplets, such as thermal ink jet, piezoelectric ink jet, acoustic ink jet, and vibrating ink jet systems. Each of these types of ink jet systems are known as drop-on-demand systems. Besides drop-on-demand systems, there are also continuous stream ink jet printing systems.
In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is broken up into droplets at a fixed distance from the orifice. The individual droplets are thereafter charged and directed toward the recording medium or are recycled into the printing ink supply. In drop-on-demand systems, an ink droplet is not formed or expelled from the printer head unless the droplet is to be placed on the recording medium. Therefore, since drop-on-demand systems require no ink recovery or post-ejection treatment, drop-on-demand systems are typically somewhat simpler in construction and operation than continuous stream ink jet printing systems.
The most common types of drop-on-demand ink jet printing systems are thermal ink jet (also known as "bubble jet") systems and piezoelectric ink jet systems. In thermal ink jet printing, the energy for drop formation and ejection is generated by electrically heated resistor elements. The resistor elements heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble. Superheating of the ink far above the normal boiling point of the ink causes the bubble formation. The expansion of the bubble forces a droplet of ink out of a nozzle at a higher rate of speed toward the recording medium. After the collapse of the bubble, the ink channel proximate the resistor element refills by capillary action.
In the piezoelectric ink jet printing system, electric signals generated by a microprocessor cause vibration of piezoelectric crystals in the printer head. The vibration of the piezoelectric crystal causes formation and ejection of ink droplets from the nozzle of the piezoelectric ink jet printer head. As with thermal ink jet printing, the ink channel of the piezoelectric inkjet printer refills by capillary action after ejection of each discrete bubble.
The viscosity and surface tension of the ink used in thermal and piezoelectric ink jet printing systems directly correlates to the ability of capillary action to quickly refill the print head after ejection of each ink droplet. The optimum combination of surface tension and viscosity varies between different print heads due to varying materials of construction and varying dimensions between different print heads.
Colorants for inks printed by ink jet printing are available in the form of dyes or pigments. Accordingly, ink jet printer inks may incorporate dye(s), pigment(s), or a combination of dye(s) and pigment(s). Of these three, dye-based ink jet printer ink compositions are most widely available commercially.
Most dye-based ink jet printer ink compositions are water based and are formed by dissolving dye in an aqueous carrier or ink vehicle. Ink compositions containing water-soluble dyes are problematic for at least a couple of reasons. First, printed images formed from ink containing water-based dyes typically do not exhibit adequate water-fastness, absent incorporation of dye stabilizers in the ink composition or application of a protective coating over the printed image. Each of these protective measures add cost to the printing process and may slow the printing process. Secondly, water-based ink jet printing compositions containing water-soluble dyes are typically not suitable for use on hydrophobic recording media, such as untreated vinyl media or hydrophilic recording media that has been sized with a hydrophobic sizing agent.
As an alternative to dye-based ink jet printing inks, pigment-based ink jet printing inks may be prepared. Pigments offer the very desirable properties of enhanced water fastness and enhanced light fastness, such as enhanced resistance to degradation by ultraviolet radiation, compared to water-soluble dyes. However, careful precautions must be taken to attain a uniform pigment size particle distribution and to prevent pigment agglomeration in the ink jet composition. Furthermore, pigment particles, unlike dye molecules, are typically not chemically bound within the printed image or to the recording media.
Very little attention has been given to formulation of ink jet printing ink compositions that are suitable for use on hydrophobic recording media, such as untreated vinyl, or hydrophilic media that has been sized with a hydrophobic sizing agent. Hydrophobic media is particularly useful for outdoor applications, such as billboards, and other types of signage or printed media, outdoor or otherwise, that is exposed to water, such as rainfall or other types of precipitation. The potential for outdoor exposure of images printed on hydrophobic media to precipitation, ultraviolet radiation from the sun, and relatively large temperature variations requires that images printed on hydrophobic media have high levels of waterfastness and lightfastness and additionally requires the printed images to be highly abrasion resistant.
There are presently no available ink compositions that provide the capability of incorporating either dye, pigment, or combinations of dye and pigment, while permitting printed images based upon the ink composition to exhibit a high degree of waterfastness, a high degree of lightfastness, quick drying attributes, and high abrasion resistance. Though some inks are capable of ultimately meeting these requirements, these inks require post-treatment, such as heat treatment or ultraviolet radiation treatment, and thereby do not exhibit the requisite quick drying attributes, standing alone. Furthermore, presently available inks are typically not suitable for use with hydrophobic recording media that is most useful for outdoor applications. Thus, a need exists for an ink jet composition that may incorporate either dye or pigment and that forms a highly lightfast, highly waterfast, highly abrasion resistant, quick drying image when applied via ink jet printing on recording media, such as hydrophobic recording media.